The present invention relates to electrical busses generally, and more particularly to a branch assembly for attaching devices such busses.
It is very common today for electrical devices to communicate with one another. For example, is frequently desirable to allow devices that receive information to pass that information to a controlling device for logging and/or processing. The processing device can then pass control commands to another device.
A thermal system is a prime example of a series of devices that need to communicate with another. A plurality of temperature acquisition devices are strategically located throughout the system, each having some type of temperature sensor (e.g. thermocouple, RTD) directly attached thereto. The temperature acquisition devices send temperature data back to one ore more control systems. Some of the control systems may be used for remote monitoring purposes only, while others may actively control the thermal processes. The active control systems then send command signals to power supplies, each having one or more electrical heaters attached thereto.
This communication among the different devices is typically done on electrical busses. The busses comprise a series of electrical conductors that run from one device to the next. Each of the conductors may have a different purpose. Some may be used to control the communication process, while others may be used to send bits of binary data. Still other conductors are sometimes needed for electrical grounding purposes.
Many bus designs and communication protocols for the same are conventional and standard. Some examples of well-known standardized bus designs include RS-232, RS-422, RS-423, and RS-485. Each of these standards, which are maintained by the Electronic Industries Association (EIA) and/or the Telecommunications Industry Association (TIA), specify a certain number of conductors in the bus, how devices (or xe2x80x9cnodesxe2x80x9d) on the bus may connect to the bus, and several other similar operating parameters.
Some bus designs, such as RS-485, allow multiple nodes on the same bus. The ideal configuration for such buses is to have the conductors run from one node to only one other node in a given line (xe2x80x9cdaisy chainedxe2x80x9d). Although in theory there should be no branches at all, in practice every time a node is placed on the bus a short branch, known as a stub, is inevitably created. The stubs on an RS-485 bus should be kept as short as possible, and should never exceed 6 inches. Configurations that violate this rule may still work, but are prone to frequent communication problems. Examples of proper RS-485 configurations are located in Ten Ways to Bulletproof RS-485 Interfaces (National Semiconductor Application Note 1057) published by the National Semiconductor Corporation in October 1996.
In the past, it has been known to include multiple bus connection points on devices. To connect the device to the bus, the conductors coming from the previous device are attached to one connection point on the new device and the conductors from the next device are attached to the other connection point. One obvious disadvantage of this connecting method is that anytime a new node/device is added to the bus, bus wiring must be rerouted. It also requires the devices to be built with the multiple connection points. Furthermore, the multiple connection points necessarily means that there is a small stub on the last device. This stub at the end of the bus must be electrically terminated for the bus to function properly at high data transmission speeds.
Another solution has been to use repeaters along the bus at branch points. Each repeater must have a separate power source, however. That is not only inconvenient, but sometimes not even feasible.
It is in view of the above problems that the present invention was developed.
The invention thus has an object to provide a quick and easy connector for communication busses that leaves practically no stubs.
It is another object of the present invention to allow the addition or removal of devices from a communication bus with minimal interruption to the bus.
It is a further object of the present invention to provide means for attaching portable devices to a communication bus without the need for power consuming devices such as repeaters.
In keeping with the above objects, the present invention is a branch assembly for a communication bus that automatically reroutes the bus when a node is added or removed. The assembly comprises a housing with three connection points and an integral switch. Two of the connection points are for the main bus interface. The remaining connection is a branch interface for the optional addition of a new branch to the bus configuration. The addition at the branch interface may be a single node, or it may be a long series of nodes already properly connected.
An integral switch which is actuated by the addition or removal of a connector at the branch interface reroutes the connectors in the assembly accordingly. When no connector is located at the branch interface, the switch remains in a closed position, allowing the conductors at the bus interfaces to be directly connected to one another. Likewise, when a connector is located at the branch interface, the switch opens. This forces the electrical circuit of the conductors to pass through the new branch or node in its path from one bus interface to the other.